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Top-down control over visual-contrast sensitivity


de la Rosa,  S
Department Human Perception, Cognition and Action, Max Planck Institute for Biological Cybernetics, Max Planck Society;

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de la Rosa, S., Schneider, B., & Gordon, M. (2007). Top-down control over visual-contrast sensitivity. Poster presented at 30th European Conference on Visual Perception, Arezzo, Italy.

The visual system is able to adjust its contrast sensitivity to the ambient contrast level. Others have shown that this adjustment is driven by stimulus parameters in a bottom - up fashion and higher order processes by means of attention. We present evidence that contrast sensitivity is under true top - down control. We paired an absolute identification paradigm with a cueing paradigm to measure identification accuracy for four low-contrast stimuli that were intermixed with an occasional high-contrast stimulus. Foreknowledge of the presentation of the high-contrast stimulus was manipulated by presenting valid and invalid cues. In experiment 1 we found that identification and discriminability of low-contrast stimuli was impaired only when the occurrence of the high-contrast stimulus was unpredictable but not when it was predictable. Only a top - down gain-control mechanism whose functions were to maximize discriminability while protecting the system from overload was consistent with the results. Experiment 2 p rovided further support for the idea that an important function of gain control is to protect visual mechanisms from overload.